The present invention relates to a method manufacturing semiconductor substrates. Specifically, the present invention provides a novel method of manufacture.
A substrate for a semiconductor module generally includes a metal sheet such as copper sheet cladded onto a ceramic plate. It is known to metallize a surface of the ceramic plate by coating it with molybdenum paste and to then attach to it a previously formed circuit pattern stamped copper sheet, or molybdenum disc of prescribed shape by brazing the preformed metal sheet to the ceramic.
There is a problem with substrates formed in this manner. The thermal expansion coefficients of the metallic sheet and ceramic plate are different. When electronic components (such as silicon pellets) are mounted on the substrate, the ceramic plate and metallic sheet are heated and there is a tendency for the substrate to crack and split.
In addition to this functional problem of cracking and splitting during circuit component mounting, it is somewhat difficult and expensive to manufacture the substrate. The process of bonding via metallizing is a complicated process. This general type of manufacture is disclosed in U.S. Pat. No. 3,994,430--Cusano et al (Nov. 30, 1976), the teachings of which are incorporated herein by reference as if fully reproduced. A semiconductor module substrate produced according to the known process, described above, is shown in FIG. 9 of Cusano '430.
An alternative to the method taught in Cusano '430 includes the steps of stamping a copper sheet to a prescribed pattern, putting the patterned copper sheet into contact with the ceramic plate and placing it in a furnace to bond the copper sheet and the ceramic plate directly by heating. With a substrate produced by such a method, since the thermal expansion coefficient of the metallic sheet is close to that of the ceramic plate, the problem of splitting is minimized where parts such as silicon pellets are mounted directly onto the copper sheet. However with this alternative method there is the disadvantage of poor precision because prestamping copper plate to a complex shape is quite difficult.